JPH08336297A - Stepping motor - Google Patents

Abstract

PURPOSE: To prevent a false signal from being outputted from a magnetoelectric conversion element due to reverse step rotation occurring upon conduction of a phase coil when the rotor is stopped by an external obstacle without requiring any intricate circuit means. CONSTITUTION: A magnetoelectric conversion element detects step rotation of the pole or pole tooth of a rotor 8 and outputs a signal voltage which is then binarized by a binarization circuit to produce a pulse voltage. When an exciting voltage is applied sequentially to phase coils in a direction to rotate the rotor 8 toward a stopper for stopping the rotor 8 at a forcibly stopping position, the rotor 8 is rotated in reverse step to a reverse step position located one step in front of the stop position. Location (f) of the magnetoelectric conversion element is set such that the variation of signal voltage thereof does not exceed the threshold value of binarization circuit before and after the reverse step rotation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stepping motor, and more particularly to a stepping motor incorporating a magnetoelectric conversion element for detecting a step rotation of a rotor.

[0002]

2. Description of the Related Art In a conventional stepping motor, a magnetoelectric conversion element that detects a step rotation of a magnetic pole or a pole tooth of a rotor and outputs a signal voltage, and a signal voltage that is output from the magnetoelectric conversion element are binarized. There is known a magnetoelectric conversion element built-in type including a binarization circuit. In this specification, a magnetic pole means an N pole or an S pole of a permanent magnet,
The pole teeth mean a gear-shaped convex portion of the rotor of the HB type or VR type stepping motor.

[0003]

When the rotation of the rotor in one direction is stopped by an external obstacle, the pattern of the exciting voltage is periodically changed so as to further rotate in the one direction. Although the rotor is blocked by an obstacle and is not actually rotating in the one direction described above, a false signal output state in which a pulse is output from the magnetoelectric conversion element may appear. This has been a troublesome problem for detecting the rotation angle.

This phenomenon causes so-called step-out when the combination of applied excitation voltages (hereinafter, also referred to as an excitation phase) is changed as it is even after the stepping motor is stopped, and further in the reverse direction by one step. It is caused by rotating (hereinafter, also referred to as reverse rotation). The present invention has been made in view of the above problems, and prevents the output of a false signal from a magnetoelectric conversion element when a phase coil is energized while a rotor is stopped by an obstacle without employing complicated circuit means. To provide a possible stepping motor,
Its purpose is.

[0005]

The first structure of the present invention is as follows.
A plurality of stator cores having induction poles arranged at the tip portion at a constant pitch in the circumferential direction, a plurality of phase coils wound around each stator core, and magnetic poles facing the induction poles at a constant pitch in the circumferential direction. Alternatively, the rotor is provided with pole teeth and is rotatably held in the circumferential direction, and a signal voltage is provided so as to face the magnetic poles or pole teeth of the rotor to detect step rotation of the rotor. In a stepping motor including a magnetoelectric conversion element that outputs a signal and a hysteresis-type binarizing circuit that binarizes the signal voltage by a pair of threshold voltages, the magnetoelectric conversion element is a reverse rotation of the rotor. Sometimes, the stepping motor is arranged at a circumferential position where the output voltage of the binarizing circuit does not change.

A second structure of the present invention is the same as the first structure, wherein the magnetoelectric conversion is performed in a stable state of the rotor during a period in which the signal voltage decreases and a period in which the signal voltage increases in accordance with the rotation of the rotor. The signal voltage of the element is set to be higher than one of the threshold voltages and lower than the other one. A third configuration of the present invention is the PM type stepping motor according to the first or second configuration, wherein the magnetoelectric conversion element is disposed near a boundary between the N pole and the S pole of the rotor in which the magnetoelectric conversion element stands still at a stable position. It is characterized by being.

A fourth structure of the present invention is the above-mentioned first or second structure.
In the above configuration, the magnetoelectric conversion element is further arranged alternately in the circumferential direction on the rotor stationary at a stable position, and is arranged in the vicinity of a mountain / valley boundary line of pole teeth magnetized by a permanent magnet. It is characterized by being. According to a fifth aspect of the present invention, in the first or second aspect, the magnetoelectric conversion elements are alternately arranged in the circumferential direction on the rotor stationary at a stable position and magnetized by the phase coil. VR arranged near the mountain / valley boundary line of pole teeth
It is a type stepping motor.

[0008]

In the first configuration of the present invention, the magnetoelectric conversion element detects the step rotation of the magnetic pole or the induction pole of the rotor and outputs the signal voltage. The binarization circuit binarizes this signal voltage with a pair of threshold voltages and outputs it as a pulse voltage. When the rotor cannot rotate in the direction that it has been rotating until now (also called the scheduled rotation direction) and stops at a predetermined stop position, further excitation is performed to rotate the rotor in this scheduled rotation direction. When the phase is changed, the rotor reversely rotates from the stop position to the reverse rotation position one step before when the excitation phase changes from the predetermined phase to the next predetermined phase.

In this configuration, the magnetoelectric conversion element is arranged at a spatial position where the change in the signal voltage output from the magnetoelectric conversion element during the reverse rotation does not exceed the threshold voltage of the binarization circuit in the signal change direction. To do. With this configuration, the binarization circuit does not output a false pulse even when the rotor rotates in the reverse direction, so that an excellent effect of not erroneously recognizing the rotor rotation angle and the timing thereof can be obtained. Further, according to this solving means, it is not necessary to add a false signal removing circuit to the binarizing circuit, and the circuit configuration becomes simple.

According to the second structure of the present invention, in the first structure, the signal voltage of the magnetoelectric conversion element is set to the threshold voltage in both the stable condition of the rotor during both the decreasing period and the increasing period of the signal voltage. Since the voltage is set to be larger than one of the voltages and smaller than the other, the output voltage of the binarization circuit does not fluctuate even if the reverse rotation occurs in the rotor stable state.

In a third structure of the present invention, the first structure is applied to a PM type stepping motor. Then, when the magnetoelectric conversion element is in the stable state of the rotor, the N pole and S
It is arranged close to the boundary with the pole. If you do this,
The above first and second effects can be easily realized in the PM type stepping motor. In the fourth or fifth configuration of the present invention, the first configuration is applied to an HB type or VR type stepping motor. In this case, since the boundary between the N pole and the S pole in the PM type corresponds to the edge of the pole tooth in the HB type or VR type, that is, the valley boundary, the magnetoelectric conversion element is the edge of the pole tooth in the rotor stable state, that is, the valley boundary. Is disposed in close proximity to. With this configuration, the first and second effects can be easily realized in the HB type or VR type stepping motor.

[0012]

【Example】

(Embodiment 1) An example of a stepping motor with a built-in magnetoelectric conversion element of the present invention will be described with reference to the drawings. Figure 1 shows a 4-phase PM step motor driven by 2-phase excitation (2-phase excitation 4
2 shows a drive circuit of the motor of FIG. 1, and FIG. 3 shows a timing chart of the excitation voltage of the motor of FIG.

This stepping motor is a so-called claw pole type stepping motor, and inside the casing 1 which also serves as a yoke portion of the stator core, the phase coils 2 and 3 are housed adjacently on a bobbin. . Adjacent to both end faces of the phase coil 2, the side wall portion 40 of the stator core,
50 are individually arranged, and the side wall portions 40 and 50 together with the casing 1 form a magnetic circuit of the phase coil 2. Side wall portions 60 and 70 of the stator core are individually arranged adjacent to both end surfaces of the phase coil 3, and the side wall portions 60 and 7 are provided.
Reference numeral 0 constitutes the magnetic circuit of the phase coil 3 together with the casing 1. Claw-shaped induction poles 4 and 5 are axially projected from the radially inner ends of the side wall portions 40 and 50 so as to cover the inner peripheral surface of the phase coil 2. They are arranged alternately at a constant pitch. Similarly, claw-shaped induction poles 6 and 7 are axially projected from the radially inner ends of the side wall portions 60 and 70 so as to cover the inner peripheral surface of the phase coil 3, and the claw-shaped induction poles 6 and 7 are provided. Are alternately arranged in the circumferential direction at a constant pitch. 8
Is a rotor, and is a cylindrical portion 81 fitted to the rotating shaft 80.
And a magnet cylindrical portion 82 made of a permanent magnet fitted to the outer peripheral surface of the cylindrical portion 81. The surface of the magnet cylindrical portion 82 is magnetized into N poles and S poles alternately in a circumferential direction with a constant width.
Each N pole and S pole is magnetized with a constant width in the axial direction. 9
Is a magnetoelectric conversion element composed of a Hall element, and faces the outer circumferential surface of the magnet cylindrical portion 82 at one end in the axial direction with a minute gap.

The phase coils 2 and 3 are driven by the four-phase excitation voltage generated by the drive circuit shown in FIG. The first-phase excitation voltage is a voltage formed by turning on the transistors T1 and T1 ′, and is hereinafter also simply referred to as the first phase. The second-phase excitation voltage is a voltage formed by turning on the transistors T2 and T2 ′, and is hereinafter also simply referred to as the second phase. Third
The phase excitation voltage is a voltage formed by turning on the transistors T3 and T3 ', and is hereinafter also simply referred to as the third phase. The fourth-phase excitation voltage is a voltage formed by turning on the transistors T4 and T4 ′, and is hereinafter also simply referred to as the fourth phase.

The application sequence of the excitation voltage of the phase coils 2 and 3, that is, the excitation voltage pattern will be described with reference to the timing chart of FIG. The excitation voltage pattern of this embodiment employs a so-called two-phase excitation method of a four-phase stepping motor, and a predetermined two of the first to fourth phases are always applied to the phase coils 2 and 3. Therefore, in order to rotate the rotor in a predetermined direction, the first phase and the second phase are the phase coils 2,
The (1 + 2) phase applied to the phase coil 3, the second phase and the third phase are applied to the phase coils 2 and 3, the (2 + 3) phase, and the third phase and the fourth phase are applied to the phase coils 2 and 3. The (3 + 4) phase, the fourth phase and the (4 + 1) phase in which the fourth phase and the first phase are applied to the phase coils 2 and 3 may be applied in this order. That is, (1+
When the 2) phase, the (2 + 3) phase, the (3 + 4) phase, and the (4 + 1) phase are applied to the phase coils 2 and 3 in this order, the claw-shaped induction pole 4
The center position of the composite N pole and the center position of the composite S pole of the stator formed by 7 to 7 are displaced in the circumferential direction by one claw-shaped induction pole pitch, whereby the rotor is rotated corresponding to the one claw-shaped induction pole pitch. Rotate only a corner (step).

FIG. 4 shows pole teeth of the stator, that is, claw-shaped induction poles.
Exciting magnetic pole characteristics of 4 to 7 and stable positions of the N pole and S pole of the rotor
(Also called Tep stable point) is expanded and illustrated.
In addition, S₁Is the first phase excitation state where the claw-shaped induction pole 4 is the S pole
State, S₂Is the second phase excitation state in which the claw-shaped induction pole 6 is the S pole,
S₃Is the third phase excitation state in which the claw-shaped induction pole 5 becomes the S pole, S_Four
Is the fourth phase excitation state in which the claw-shaped induction pole 7 is the S pole, N₁Claw
Phase excitation state in which the linear induction pole 5 becomes the N pole, N₂Is a nail-shaped invitation
The second phase excitation state in which the conductive pole 7 becomes the N pole, N₃Is the claw-shaped induction pole
3rd phase excitation state in which 4 is the N pole, N_FourClaw-shaped induction pole 6
This is the fourth-phase excitation state in which the pole is the N pole. N₀Is the N pole of the rotor
Is a predetermined one. In FIG. 4, (a) is (1+
2) Shows the stable point of the rotor during phase excitation, (b) is (2+
3) Indicates the stable point of the rotor during phase excitation, (c) is (3+
4) Shows the stable point of the rotor during phase excitation, (d) is (4+
1) Shows the stable point of the rotor during phase excitation. With the N pole of the rotor
The length (pole pitch) in the circumferential direction with the S pole is 4 to 7 claw-shaped induction poles.
It corresponds to two pitches. For example, (1 + 2) phase excitation
Then the magnetic pole N of the rotor₀The center position of is S of the stator₁And S
₂It is stable facing the middle position.

The position e of the conventional magnetoelectric conversion element 9 is shown in e. That is, conventionally, the magnetoelectric conversion element 9 is disposed at the circumferential center position of any one of the claw-shaped induction poles 4 to 7 (claw-shaped induction pole 6 in FIG. 4). The position of the magnetoelectric conversion element 9 in the present embodiment is shown in f. That is, in this embodiment, the magnetoelectric conversion element 9 is arranged at the circumferential intermediate position between the two circumferentially adjacent claw-shaped induction poles (the circumferential intermediate position between the claw-shaped induction poles 6 and 5 in FIG. 4). . Therefore, in this embodiment, the magnetoelectric conversion element 9 is arranged on the boundary line between the N pole and the S pole of the rotor in the stable state of the rotor during (1 + 2) phase excitation and (3 + 4) phase excitation.

The signal voltage V output from the magnetoelectric conversion element 9
As shown in FIG. 5, s is binarized by a Schmitt trigger (binarization circuit in the present invention) 10 and converted into a pulse voltage Vp. FIG. 6A shows the signal voltage Vs when the magnetoelectric conversion element 9 is set to the position f (the position of this embodiment), and the magnetoelectric conversion element 9 is set to the position e (the conventional position). The signal voltage Vs' is shown in FIG. 6 (b).
Here, the intermediate level A is the output voltage when the magnetoelectric conversion element 9 is located on the boundary line between the N pole and the S pole of the rotor,
It is 0V in the magnetoelectric conversion element 9 in which the Hall element is incorporated in the bridge circuit. VtH is Schmitt trigger 1
0 is a threshold voltage when the low level (0) is switched to the high level (1), and VtL is a threshold value when the Schmitt trigger 10 is switched from the high level (1) to the low level (0). Voltage. The threshold voltage VtH is a predetermined voltage ΔV (for example, the signal voltage Vs from the intermediate level A).
Of 10 to 15% of the maximum value of)
The threshold voltage VtL is a predetermined voltage Δ from the above intermediate level A.
It is negatively shifted by V (for example, 10 to 15% of the maximum value of the signal voltage Vs). (C) is a waveform of the pulse voltage Vp obtained by binarizing the signal voltage Vs by the Schmitt trigger 10, and (d) is a waveform of the pulse voltage Vp 'obtained by binarizing the signal voltage Vs' by the Schmitt trigger 10.

Next, at the rotation angle position where the rotor rotates in the forward rotation direction, the obstacle S is excited while the further rotation in the forward rotation direction is forcibly stopped (forced step out). The behavior (pulsation) of the rotor when a voltage is applied will be described with reference to FIGS. 7 and 8. FIG. 7 is a development view showing the relative positional relationship between the claw-shaped induction poles 4 to 7 and the N pole and S pole of the rotor in each excitation phase, and FIG. 8 is a timing chart showing the time change of the rotation angle of the rotor. is there.

(A) shows the rotor stable state in the (1 + 2) phase excitation state, (b) shows the rotor position in the (2 + 3) phase excitation state, and (c) shows the rotor position in the (3 + 4) phase excitation state. (D) shows the rotor position in the (4 + 1) phase excitation state. In this example,
N of rotor in stable state in (1 + 2) phase excitation
The rotation of the pole and the S pole in the normal rotation direction is stopped by the obstacle S.

When the excitation voltage is (1 + 2) phase excitation, it becomes (2+
3) Even if shifting to phase excitation, the rotor cannot rotate normally due to the restriction of the stopper S, and the excitation voltage changes from (2 + 3) phase excitation to (3
When shifting to +4) phase excitation, the rotation torque acting on the rotor becomes 0, the rotor does not rotate, and the excitation voltage becomes (3+
4) When the phase excitation is shifted to the (4 + 1) phase excitation, a rotational torque is generated in the rotor in the reverse rotation direction and only the rotor is reversely rotated, and the pitch of one claw-shaped induction pole 4 to 7 (1 step) Reverse rotation only). And the excitation voltage is (4+
1) When the phase excitation is shifted to the (1 + 2) phase excitation, a rotational torque is generated in the rotor in the forward rotation direction, the rotor is normally rotated, and the pitch (1) of one claw-shaped induction pole 4 to 7 is generated. Forward rotation by (step rotation angle) returns to the state of (a). That is, when the excitation voltage is applied in the direction of rotating toward the stopper S while the rotation of the obstacle S is stopped, the reverse rotation (reverse rotation) of one step and the return operation thereof are performed only once in one cycle period. You can see that it will occur.

Changes in the signal voltage Vs of the magnetoelectric conversion element 9 and the pulse voltage Vp obtained by binarizing the signal voltage Vs during the reverse rotation will be described with reference to FIGS. 7 and 6. 7 (a),
During the periods (b) and (c), the signal voltage Vs of the magnetoelectric conversion element 9 set to f (see FIG. 4) is at the level A (for example, 0 V) at the point P1 (FIG. 6) because the rotor is stopped. See). Next, in the period of changing from (c) to (d) of FIG. 7 and returning to (a), the signal voltage Vs changes to P2 point (see FIG. 6) and then returns to P1 point again. That is, when the rotor is forcibly stopped in the stable state during the (1 + 2) phase excitation, and then the excitation voltage is further applied in the forward direction, the magnetoelectric conversion element 9 does not output a signal indicating the rotation of the rotor.

Next, as a comparison with this embodiment, FIG. 7 and FIG. 7 show changes in the signal voltage Vs ′ of the conventional magnetoelectric transducer set to e and the pulse voltage Vp ′ obtained by binarizing the signal voltage Vs ′ by the Schmitt trigger 10. 6 will be described. During the periods (a), (b), and (c) of FIG. 7, the signal voltage Vs ′ of the magnetoelectric conversion element 9 set to e (see FIG. 4) is stopped at the P1 ′ point (see the figure) because the rotor is stopped. 6)).
Next, in the period of changing from (c) to (d) of FIG. 7 and returning to (a), the signal voltage Vs changes to the point P2 ′ (see FIG. 6) and then returns to the point P1 ′ again. . here,
Since the potential drop of the signal voltage Vs 'from the P1' point to the P2 'point exceeds the threshold voltage VtL, the pulse voltage Vp' changes from the high level (1) to the low level (0). Also, after that, the signal voltage Vs ′ from the point P2 ′ to the point P1 ′
Rises above the threshold voltage VtH, the pulse voltage Vp 'changes from low level (0) to high level (1). After all, when the magnetoelectric conversion element 9 is set to the position e, when the rotor is forcibly stopped in the stable state during the (1 + 2) -phase excitation and then the excitation voltage is further applied in the forward rotation direction, once in one cycle period of the excitation voltage. It can be seen that one pulse voltage is output.

(Modification 1) In the above embodiment, the rotor is forcibly stopped by the stopper S at a position where the rotor is in a stable state during (1 + 2) phase excitation ((a) in FIG. 7). Is not limited to this. That is, the rotor is forcibly stopped by the stopper S at a position where the rotor is in a stable state at the time of (2 + 3) phase excitation, and at this time, the magnetoelectric conversion element 9 is arranged near the center in the circumferential direction of the N pole or S pole of the rotor. Also,
The same effect as that of the first embodiment can be obtained. In this case, it can be seen that the signal voltage Vs at the point P2 shown in FIG. 6 is output at the position stopped by the stopper S, and by reverse rotation, it moves back 90 degrees to return to the point P3, and then returns to the point P2 again. . In this case, the pulse voltage Vp is at the low level (0) at P2 and remains at the low level (0) thereafter.

After all, it can be seen that the false signal is output only when the signal voltage Vs changes by overcoming both of the two threshold voltages VtH and VtL of the Schmitt trigger 10 by the reverse rotation of 90 degrees. . Therefore, when the rotor is in a stable state at the position where it is forcibly stopped by the obstacle S by applying some excitation voltage, the magnetoelectric conversion element 9 is set near the boundary line between the N pole and the S pole of the rotor. The same effect as 1 can be obtained.

Taking all of these into consideration, the N pole and the S pole in the stable state of the rotor when the excitation voltage of an arbitrary pattern is applied.
It can be seen that the magnetoelectric conversion element 9 may be set near the boundary line with the pole (see FIG. 4). (Modification 2) It is possible even when the four-phase PM step motor is driven by one-phase excitation, and in this case as well, N in the stable state (step stable point) of the rotor when the excitation voltage of an arbitrary pattern is applied. The magnetoelectric conversion element 9 may be set in the vicinity of the boundary line between the pole and the S pole.

The basics are the same for the n-phase multi-phase motor, and the magnetic field is near the boundary line between the N pole and the S pole in the stable state (step stable point) of the rotor when the excitation voltage of an arbitrary pattern is applied. The conversion element 9 may be set. next,
In the VR type stepping motor (when the rotor is not a permanent magnet), for example, when a suitable magnetoelectric element carrying a backup magnet is made to face the pole teeth of the rotor, the signal voltage Vs of the magnetoelectric conversion element 9 becomes an intermediate level in FIG. A has a characteristic including a predetermined DC bias voltage. Also in this case, the piping position of the element can be determined according to the concept of the PM type. That is, the magnetoelectric element may be arranged in the vicinity of the boundary line (intermediate point of the slope) of the pole teeth of the rotor at the step stable point when the excitation voltage of an arbitrary pattern is applied. That is, the mountain-valley boundary line corresponds to the boundary line between the N pole and the S pole in the PM type. FIG. 9 shows the arrangement position of the magnetoelectric conversion element in the VR type stepping motor.

Next, the same applies to the HB type step motor, and when the magnetoelectric conversion element carrying the backup magnet on its side faces the pole teeth of the rotor, the signal voltage V of the magnetoelectric conversion element 9 is generated.
s has a characteristic that the intermediate level A in FIG. 6 includes a predetermined DC bias voltage. Also in this case, the arrangement position of the element can be determined according to the concept of the PM type.
That is, the magnetoelectric element may be arranged in the vicinity of the boundary line (intermediate point of the slope) of the pole teeth of the rotor at the step stable point when the excitation voltage of an arbitrary pattern is applied. FIG. 10 shows the arrangement position of the magnetoelectric conversion element in the HB type stepping motor.

[Brief description of drawings]

FIG. 1 is an axial sectional view of a stepping motor according to an embodiment.

FIG. 2 is a circuit diagram of a drive circuit of the stepping motor of FIG.

3 is a timing chart showing changes in an excitation voltage generated by the drive circuit of FIG. 2 and a rotation angle of a rotor.

FIG. 4 is a development view showing the relationship between the pole teeth of the stator, that is, the exciting magnetic polarities of the claw-shaped induction poles 4 to 7 and the stable positions (also referred to as step stable points) of the N and S poles of the rotor.

FIG. 5 is a circuit diagram showing a circuit for detecting rotation of a rotor.

FIG. 6 shows (a) a signal voltage Vs when the magnetoelectric conversion element 9 is set to the position f of this embodiment, and (b) shows a signal voltage Vs ′ when the magnetoelectric conversion element 9 is set to the conventional position e.
The waveform of the pulse voltage Vp obtained by binarizing the signal voltage Vs by the Schmitt trigger 10 is shown in FIG.
A pulse voltage V obtained by binarizing s'with a Schmitt trigger 10.
The waveform of p'is shown in (d).

FIG. 7 is a development view showing the behavior of the rotor when the rotor is forcibly stopped by a stopper S and an excitation voltage is applied.

8 is a timing chart of the rotor rotation angle showing the behavior of the rotor shown in FIG. 7 when the rotor is forcibly stopped and an excitation voltage is applied.

FIG. 9 is a development view showing the relationship between the exciting pole characteristics of the pole teeth of the stator, that is, the claw-shaped induction poles 4 to 7 and 4a to 7a, and the stable position of the rotor and the position of the magnetoelectric conversion element in the VR stepping motor.

FIG. 10 is a development view showing the relationship between the magnetic poles of the stator of the HB stepping motor, that is, the exciting magnetic polarities of the claw-shaped induction poles 4 to 7, 4a to 7a, and the stable position of the rotor, and the position of the magnetoelectric conversion element.

[Explanation of symbols]

Reference numerals 2 and 3 are phase coils, 4 to 7 are claw-shaped induction poles (induction poles of the stator core), 8 is a rotor, 9 is a magnetoelectric conversion element, 10 is a Schmitt trigger (binarization circuit), and S is a stopper.

Claims (5)

[Claims] 1. A plurality of stator cores having induction poles arranged at a tip portion in a circumferential direction at a constant pitch, a plurality of phase coils wound around each stator core, and a circumferential direction facing the induction poles. A rotor in which magnetic poles or pole teeth are arranged at a constant pitch and which is rotatably held in the circumferential direction, and a rotor which is arranged so as to face the magnetic poles or pole teeth of the rotor to rotate the rotor stepwise. In a stepping motor including a magnetoelectric conversion element that detects and outputs a signal voltage, and a hysteresis type binarization circuit that binarizes the signal voltage by a pair of threshold voltages, wherein the magnetoelectric conversion element is the rotor. The stepping motor is arranged at a circumferential position where the output voltage of the binarizing circuit does not change during the reverse rotation of the stepping motor. 2. The signal voltage of the magnetoelectric conversion element is higher than one of the threshold voltages in a stable state of the rotor during a period in which the signal voltage decreases and a period in which the signal voltage increases in accordance with the rotation of the rotor. The stepping motor according to claim 1, wherein the stepping motor is set smaller than the others. 3. The stepping motor according to claim 1 or 2, wherein the magnetoelectric conversion element is arranged near a boundary between the N pole and the S pole of the rotor stationary at a stable position. 4. The stepping motor according to claim 1, wherein the magnetoelectric conversion elements are arranged alternately in the circumferential direction on the rotor stationary at a stable position and are magnetized by permanent magnets. HB type stepping motor arranged near the mountain valley boundary. 5. The stepping motor according to claim 1, wherein the magnetoelectric conversion elements are alternately arranged in a circumferential direction on the rotor stationary at a stable position and magnetized by the phase coils. VR type stepping motor disposed near the mountain valley boundary line.